Wedding Inspiration please

I've been invited to a wedding early next year...Need an 'all day' outfit.Problems - it's going to be quite 'posh' and my budget isn't; it's also my partner's family - so his ex' etc will be there. I know it's just me but I'll be feeling like a big frump anyway and I want to feel 'okay'.I'm 5'8 and size 16....all boobs and bum. Legs are badly scarred so I'd like them covered.His family are all petite, size 8/10. Help!!!!!